The invention relates to a device for centring, aligning and clamping a rigid disc in an operating position on a disc drive unit, which disc can be inscribed and/or read when rotated and has a centre hole bounded by a wall, which device comprises a drive spindle which is rotatable about an axis of rotation and which has a free end, a centring device which is rotatable with the drive spindle and which is arranged near the free end of said spindle, which centring device comprises a plurality of radially movable centring members which are pivotally connected to the drive spindle and which each comprise at least one centring surface, centring surface being pressed against said wall of the disc in the operating position of the disc, and a disc alignment means arranged on the drive spindle to align the disc in the operating position in a plane perpendicular to the axis of rotation of the drive spindle.
Such a device is disclosed in U.S. Pat. No. 4,218,065. The known device is employed in an optical player for centring, aligning and retaining an optical disc. The centring device comprises a plurality of resilient rod-shaped centring members which are radially movable between a rest position and an operating position which is situated nearer the axis of rotation, which members are moved against their resilient action when the disc is mounted onto the drive spindle through cooperation with the wall of the centre hole of the disc. The centring members have fixed ends by which they are connected to the drive spindle and they are kinked at the ends which are remote from the drive spindle. When in the rest position at a side which is situated nearer the free end of the drive spindle, the centring members together form an uniterrupted truncated cone whose transverse dimension varies from smaller to larger than the diameter of the disc hole, and in the operating position, at a side which is situated more remote from the free end of the drive spindle, they constitute an uninterrupted cylinder having a transverse dimension equal to the diameter of the disc hole.
The radially movable centring members provide a satisfactory centring of the disc and preferably a large number of centring members is used in order to reduce the influence of local irregularities in the wall of the disc hole on the centring of the disc.
A drawback of the known device is that a comparatively large force must be exerted on the video disc to bring it into its operating position. This means that the device should always be equipped with a disc pressure means which can be brought in a position opposite the centring device. The disc pressure means is constructed to exert a load, which is directed toward the disc alignment means, on the disc which is situated on the centring device, so that the disc is pressed over the centring device under radial deformation of the centring members and is subsequently clamped against the disc alignment means. The torque required for starting the disc and rotating it during operation is applied to the disc mainly by the friction between the disc alignment means and the disc.